Compact, high-efficiency, high-power solid state light source using a single solid state light-emitting device

ABSTRACT

A compact, high-efficiency, high-power, solid state light source, comprising a high-power solid state light-emitting device, a light guide having a proximal light-receiving end proximate the light-emitting device and a distal light-transmitting end spaced farther from the light-emitting device, and a mechanical light guide fixing device coupled to the light guide near its proximal end, to hold the proximal end of the light guide in position near the light-emitting device.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims priority of Provisional applicationserial No. 60/457,672, filed on Mar. 26, 2003.

FIELD OF THE INVENTION

[0002] This invention relates to a remote illumination device using ahigh-power LED and a fiber optic light guide.

BACKGROUND OF THE INVENTION

[0003] Light sources for endoscopic use are generally of two types:incandescent filament lamps and arc lamps. Incandescent lamps producelight by passing current through a tungsten filament, causing it toradiate light in proportion to its blackbody color temperature. Thehotter the filament, the higher its color temperature and the morenearly it approaches daylight with a color temperature of approximately5500K. Tungsten filament lamps range in color temperature fromapproximately 2400-3400K. Because of the low color temperature, objectsilluminated by a tungsten filament light source appear slightly yellowdue to the low output of blue light from these sources. Arc lampsproduce light by creating a plasma between two electrodes within thesealed bulb. White light from these lamps can be produced by choosingthe appropriate fill gas (usually Xe) and pressure (usually severalatmospheres). Color temperature of common arc lamps is approximately4000-6000K. Both types of lamps, filament and arc, are very inefficientin converting electrical power to light, and consequently produce largeamounts of heat. The heat must be dissipated. It also contributes to ashortened useful life of such light sources.

[0004] There have been numerous attempts to utilize low power (<1 Welectrical power consumption, typically operating below 100 mW) LEDscoupled to fiber optic light guides as light sources for endoscopy,dentistry, and for remote illumination of objects (as with aflashlight). Most of these prior attempts employ numerous low power LEDsfor remote illumination. Multiple LEDs are necessary because the lightoutput from a single, low power LED is very low and there is poorcoupling of light emitted by the LED(s) into the optical fiber. Anexample of several coupling methods appears in U.S. Pat. No. 6,331,156whereby the inventors place the fiber optic directly in front of eithera surface mount or cylindrical LED without the use of additional opticalcomponents, coatings or gel. This patent also exemplifies the use ofadditional optical components in the form of lenses or mirrors in orderto collect light generated from a standard, unmodified LED packageconfiguration. US published patent application 2004/0004846 A1 utilizesa lens to couple the light emitted by an LED into a fiber optic. USpublished patent application 2003/0156430 A1 describes a device thatconsists of a number of individual LEDs mounted on mirrors, thearrangement of the LEDs and mirrors having a common focal point at theinput end of the fiber light guide. U.S. Pat. No. 6,260,994 describes aplurality of LEDs mounted between a spherical or parabolic reflector anda lens, which directs the light emitted by the LEDs into the light guidefiber. In this invention, the LEDs emit light towards the collectinglens and away from the reflector. In U.S. Pat. No. 6,318,887, the LEDsare positioned so as to emit radiation towards a reflector, which thenreflects light through a transparent printed circuit board and towards alens and fiber light guide. In US published patent application2002/0120181 A1, light emitted by several LEDs is collected along acommon optical axis through a series of beam splitting prisms, in atleast one embodiment with the use of lenses to couple the light from theLED into the prism, and then into the fiber. In these examples, the LEDpackages are not modified; multiple, low power LEDs are employed inorder to attain a reasonable level of illumination; and in most of theseexamples, external optical components are employed in order to increasethe coupling efficiency between the LEDs and the light guide fiber.

[0005] In US published patent application 2003/0231843, numerous lowpower LEDs are coupled into individual fibers, which are combinedtogether at the distal end of the device to produce intense light forcuring dental epoxy. This patent application describes an approach inwhich the LED package and light guide fiber are modified in order toincrease the optical coupling efficiency between the two. In oneembodiment, the cladding material from the fiber is removed and thefiber core is placed within the LED epoxy lens. The exterior of theepoxy lens is coated with a low refractive index “clad” that producestotal internal reflection of the light emitted by the LED. Some of thelight reflected by this LED clad can make its way into the core of thefiber and be transmitted to the distal end of the device. This patentapplication also includes a description of a taper attached to theexternal surface of the LED dome lens that couples the light into thefiber. Again, however, additional optical elements (cladding or tapersapplied to the LED) are used. Also, the device employs numerous lowpower LEDs to attain sufficient light output from the device. This typeof arrangement would be difficult if not impossible to implement with ahigh power LED because of the high operating temperature of these LEDs(up to 135 degrees C.). At high temperatures, the epoxy used in typicalLED packages will melt or crack due to thermal cycling. In addition,high temperatures will cause the epoxy to discolor, typically becomingyellow. This will impart a yellow cast to the light, thereby loweringits effective color temperature and its desirability as a visual lightsource. In addition, discoloration will absorb lower wavelengths oflight emitted by the LED, particularly those wavelengths in the blue andUV region of the spectrum that are essential for epoxy curing andfluorescence applications.

SUMMARY OF THE INVENTION

[0006] Recent advances in light emitting diodes (LEDs) have seen theadvent of very high power LEDs, up to 5 W. This invention utilizes ahigh power white light LED as a light source for medical and industrialendoscopes. The high power, very small size, and high efficiency ofthese devices makes it possible to design an untethered endoscope; anendoscope without a light guide umbilical connecting the endoscope to anexternal light source.

[0007] The invention entails an endoscope with a battery powered, highpower LED incorporated into the endoscope handle. A light guide isclosely coupled to the LED, without the need for additional opticalcomponents. Accordingly, a large percentage of the light emitted by theLED is coupled directly into the light guide, which transmits this lightto the distal end of the endoscope, or any remote location, andilluminate the object under investigation. The light guide is preferablycomprised of a bundle of small diameter fibers configured to closelymatch the size and shape of the light-emitting surface of the LED.

[0008] Several innovative designs for coupling a light guide fiberbundle to the LED are described that produce a sufficient amount oflight for illuminating the object. These designs do not includeauxiliary optics, such as lenses or mirrors, but rely on the small sizeof the LED's emitting region and the placement of the light guidedirectly against the light emitting region. The use of an optical indexmatching material between the LED's emitting region and the light guidecan, in some cases, improve the transfer efficiency of light out of theLED chip into the light guide. Because the LED itself is very efficientin converting electrical energy into light, and the described opticalinterface is very efficient at coupling this light from the LED into thelight guide, this new light source can be powered by small batteriesthat will operate for a considerable length of time without the need forbattery replacement or recharging, and without making the endoscopehandle cumbersome or unwieldy. The lack of the need for additionaloptical components simplifies the mechanical design and volume occupiedby the light source.

[0009] The high light output and high coupling efficiency of the lightemitted by the LED into the light guide increases battery lifetime, orpermits the use of smaller capacity, and smaller volume, batteries. Theinvention could use more than one LED in cases in which there isinsufficient light from a single LED and there is sufficient room withinthe housing to add one or more additional LEDs, which would be coupledto the light guide in the manners described herein. Also, other types ofLEDs can be coupled to light guides in a similar manner as is describedherein, particularly LEDs with different spectral outputs (such as UV,430 nm, 470 nm, 530 nm, near infrared, infrared, etc.), LEDs produced byother manufacturers (such as Nichia, Microsemi, etc.), and LEDs withdifferent form factors (such as the flat Microsemi OPTO3 package, roundor cylindrical LED package (T1, T1-¾, etc.), or small surface mountpackage).

[0010] The preferred embodiment of this invention relates specificallyto medical and industrial endoscopes, both flexible and rigid. However,this invention also has applications in other areas, such as: fiberoptic lighting; delivery of light from other regions of the spectrum,such as the ultraviolet, near infrared, and infrared; and other types ofoptical observations such as fluorescence, absorbance, and transmittancemeasurements. Additionally, this light source device can be used as aremote light source (fiber optic flashlight) for visual inspection. Thisfiber optic and LED light source can also be made explosion proofbecause of its low voltage, low power consumption, and small volume;details of this would be apparent to those skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Other objects, features and advantages will occur to thoseskilled in the art from the following description of the preferredembodiments, and the accompanying drawings, in which:

[0012]FIG. 1 is a greatly enlarged partial cross sectional diagram ofthe preferred embodiment of the high power LED-based light source of theinvention;

[0013]FIG. 2 is a similar diagram for an alternative embodiment of theinventive light source;

[0014]FIG. 3 is a similar diagram of yet another alternative embodimentof the light source of this invention; and

[0015]FIG. 4 is a similar view of another embodiment of the inventivelight source.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The preferred embodiment of this invention utilizes a high powerLED (Luxeon III Model LXHL-LW3C, Lumileds Lighting, LLC, 370 W. TrimbleRoad, San Jose, Calif. 95131) with a typical forward voltage of 3.7V andoperating current at 700 mA. This device can be safely operated up to acurrent of 1A with a corresponding typical forward voltage of 3.9V. Thiswhite LED has a typical color temperature of 5500K. The LED chip has anemitting surface of approximately 1 mm×1 mm, and is coated with awavelength conversion phosphor (and/or fluorophor) that emits abroadband continuum of visible white light between about 470-700 nm.

[0017] The light emitting area of the LED is coupled to a small 1 mmsquare or round bundle of light guide fibers; a typical light guidebundle size used in endoscopes. The light guide bundle is composed ofhundreds of individual glass (or plastic) fibers grouped together toform a single bundle at the light source, and either a single bundle ormultiple bundles at the distal end of the endoscope. Such bundles cantake on a variety of shapes at the distal end depending upon the designof the particular endoscope: one or more round bundles, a circular halo,a crescent, or the like. Small diameter fibers, typically 30-50micrometers in diameter, are employed because these small fibers areflexible (necessary for flexible endoscopes that bend during use), orbecause they are required to fit into the narrow spaces around theoptics either in the shaft or distal head of the endoscope.

[0018] Other types of light guides can be coupled to the LED in themanners described herein, including: liquid light guides, plastic orglass fibers, plastic or glass rods, and tapers made from fibers (glassand plastic) or solid tapers (glass and plastic). Single glass orplastic fibers may comprise the light guide. Such fibers around 1 mm indiameter are typically flexible. In order to accommodate a small lightguide bundle of less than the LED emitting area, a fiber optic or solidplastic or glass taper may be placed between the LED emitting surfaceand the bundle, acting as an adapter that captures substantially all ofthe light emitted from the LED and efficiently couples it into the fiberbundle that delivers the light to the distal end of the instrument.

[0019] The details of the endoscope or other device in which the lightsource is used are known to those skilled in the art, for example asdisclosed in U.S. Pat. No. 6,260,994 (incorporated herein by reference).This holds true whether the light source is used in a medical orindustrial endoscope (either flexible or rigid) or other applicationareas such as fiber optic lighting, delivery of light from other regionsof the spectrum, other types of optical observations such asfluorescence, absorbance, and transmittance measurements, and remotelight sources akin to fiber optic flashlights, used primarily for visualinspection.

[0020] The high-power white light-emitting LED chip is commerciallysupplied encapsulated in a silicone optical gel covered by a plasticdome lens assembly, which spreads the emitted light over a 160 degreeangle (total included angle at which 90% of the total luminous flux iscaptured). A considerable amount of light can be captured by placing thelight guide at the surface of this dome lens or utilizing additionaloptical components (lenses, mirrors, tapers, etc.) to couple the lightinto the fiber bundle. However, a much larger portion of light can becaptured by moving the light guide adjacent to the surface of the LEDchip.

[0021]FIG. 1 demonstrates how the maximum coupling of light from the LEDchip into the light guide is achieved. The plastic lens and coupling gelas supplied with the LED are first removed, exposing the LED chip 600and its phosphor coating 500. LED chip 600 is supplied mounted on heatsink 700. Wires 400 supply power to LED chip 600. A bundle of polishedlight guide fibers 200 having a flat face (typically filling the entireemitting area of chip 600) is epoxied into a stainless steel ferrule100, which is ideally the same shape and size as the LED chip emittingsurface area. Other materials can be used for the construction of theferrule, such as other metals, alloys, and plastics, or the ferrule canbe eliminated altogether when not needed for grouping a large number offibers together (such as when a single, large diameter fiber or rod isused instead of a group of fibers). The end of ferrule 100 can becoincident with the light guide 200 face, or can be slightly recessedfrom the face of the polished light guide 200 in order to reduce thesize of the end of this light guide. The polished light guide 200 faceis placed in contact with the surface of LED chip 600, or as close tothis surface as mechanically possible. Ideally, both faces are as flatas possible, which accomplishes actual contact or very minute separationacross all or a substantial portion of the interface between the LEDsurface and the face of the light guide. The flexibility of the lightguide fibers can assist in a higher degree of contact between the twofaces. This ensures the most efficient coupling of light out of LED chip600 into light guide 200.

[0022] Other embodiments of the invention are also anticipated and arenow described. FIGS. 2 and 3 demonstrate how the LED can be coupled to alight guide with little or no modification to the LED housing. In FIG.2, light guide 200 is placed directly adjacent to the LED dome lens 900.Sufficient light may be coupled into light guide 200 to illuminate theobject of interest. However, the optical transfer efficiency of thiscoupling is very poor, resulting in a lower level of illumination of theobject as compared to the preferred embodiment described above. This canbe compensated at least in part by operating at higher power, which mayincrease the light output but also lowers battery and LED lifetime.

[0023] In FIG. 3, dome lens 900 of the LED is ground and polished nearlydown to the level of internal silicone encapsulent 300, so as topreserve the integrity of the mechanical package. This increases theamount of light available to light guide 200, as the amount of lightpresent at any plane above the surface of LED chip 600 is inverselyproportional to the distance between this plane and the LED chip.Therefore, if the distance from the LED chip to the light guide'spolished face is reduced from 3 mm to 2 mm, an increase in light density(light per unit area) of 2.25 times is achieved. To further improve theamount of light coupled into light guide 200, an index matching material(not shown) can be placed between the LED's dome lens 900 and lightguide 200.

[0024]FIG. 4 depicts yet another embodiment of the invention in whichLED dome lens 900 is partially removed so as to expose the LED'ssilicone encapsulent material 300 that encapsulates LED chip 600 andphosphor 500. Light guide 200 can then be immersed in the LED's indexmatching material 300, and placed in close proximity to the emittingsurface of the LED. This can be accomplished without the need to disturbthe original index matching material 300, thereby avoiding thepossibility of introducing air bubbles within the optical path. Careshould be taken so as not to introduce air between light guide 200 andsilicone encapsulent 300. This can be accomplished by assembling thecomponents in a vacuum glove box, or by inclining light guide 200 at aslight angle when placing it in silicone encapsulent material 300. Aslight guide 200 is lowered into silicone encapsulent 300, the fiber isslowly inclined back towards perpendicularity with respect to LED chip600 without trapping air bubbles at the interface. Sleeve 1000 can thenbe inserted over ferrule 100 and the LED assembly, and fastened in placeeither with adhesives or by mechanical means. This will hold light guide200 in place and prevent silicone encapsulent 300 from flowing out ofmodified dome lens 900 at a later time. Sleeve 1000 is optional.

[0025] In some instances, it is desirable to employ an index matchingmaterial between the fiber bundle and the LED chip, or the combinationof the LED chip and its phosphor. The index matching material helps tocouple the emitted light into the light guide, and typically has anindex of refraction between that of the light emitting surface and thatof the light guide. The material can be a gel. Examples of when an indexmatching material is desirable are: when the emitting surface is asubstrate that the LED chip is mounted to, such as sapphire (n=1.76,where “n” is the refractive index), or when the LED chip is the emittingsurface and it possesses a high refractive index. Examples of LED chipswith very high refractive indices include chips manufactured fromgallium nitride (n=2.5), gallium phosphide (n=3.31), and galliumarsenide (n=4.02). The amount of light coupled into the light guide fromthe LED can be increased, potentially by up to a factor of two, when anappropriate index matching material is employed between the LED and thelight guide. The index matching material may also substitute for thesilicone encapsulent 300; the silicone encapsulent 300 being a specifictype of index matching material.

[0026] While the preferred embodiment of this invention utilizes aLuxeon III LED with a 1 mm square emitting surface, other LED packagedesigns also lend themselves to the inventive technique of capturinglight by a light guide, which may be accomplished with a fiber bundle.Some examples of these other package designs include the industrystandard T1 (3 mm) and T1-¾ (5 mm) packages in which the LED chip isenclosed in an epoxy dome lens. It is readily apparent to those skilledin the art to understand how the epoxy package can be removed down tothe level of the LED chip and coupled to the light guide. Similarly, theflat package design of the Microsemi (Microsemi Corporation, 580Pleasant Street, Watertown, Mass. 02472) UPW3LEDxx readily lends itselfto fiber coupling by directly bonding the light guide fiber to the faceof the window adjacent to the LED chip, with or without an indexmatching material between the window and the fiber as is described inFIG. 4, substituting an index matching gel for the silicone encapsulent.

[0027] Other embodiments will occur to those skilled in the art and arewithin the following claims.

What is claimed is:
 1. A compact, high-efficiency, high-power, solidstate light source, comprising: a high-power solid state light-emittingdevice; and a light guide having a proximal light-receiving end heldproximate the light-emitting device, and a distal light-transmitting endspaced farther from the light-emitting device.
 2. The light source ofclaim 1, wherein the light-emitting device comprises a light-emittingdiode (LED).
 3. The light source of claim 2, wherein the LED emits whitelight.
 4. The light source of claim 3, wherein the LED emits a broadbandvisible light including at least the 470-700 nm wavelength band.
 5. Thelight source of claim 2, wherein the LED has a light emitting area thatis about 1 mm square.
 6. The light source of claim 2, wherein the LEDcomprises a white light emitting substance that emits when excited bythe diode.
 7. The light source of claim 2, wherein the LED draws up to5W of power.
 8. The light source of claim 1, wherein the light guidecomprises a bundle of a large number of small diameter individualfibers.
 9. The light source of claim 8, wherein the fibers havediameters of about 30-50 micrometers.
 10. The light source of claim 8,wherein the fibers are made of glass or plastic.
 11. The light source ofclaim 8, further comprising a ferrule that surrounds the fiber bundle.12. The light source of claim 11, wherein the ferrule is located closeto but not at the proximal end of the fiber bundle.
 13. The light sourceof claim 1, wherein the light-emitting device defines a substantiallyflat light-emitting surface.
 14. The light source of claim 13, whereinthe proximal end of the light guide is essentially flat and is locateddirectly on the light-emitting surface of the light-emitting device. 15.The light source of claim 2, further comprising a light-conductingmaterial between the light-emitting device and the proximal end of thelight guide, the material having a refractive index between that of thelight-emitting surface and that of the light guide.
 16. The light sourceof claim 15, wherein the light-conducting material comprises asilicone-based device encapsulent material.
 17. The light source ofclaim 15, wherein the light-conducting material comprises anindex-matching gel.
 18. The light source of claim 15, further comprisinga structure that at least partially contains the material.
 19. The lightsource of claim 18, wherein the structure comprises at least part of thedome lens that surrounds the material.
 20. The light source of claim 19,wherein the dome lens is configured to have an essentially flat surfaceagainst which the proximal end of the light guide is held.
 21. The lightsource of claim 1, wherein the light guide comprises a single glass orplastic fiber.
 22. The light source of claim 1, wherein the light guidecomprises a fiber optic or solid taper coupled to a large number ofsmall diameter light guide fibers.
 23. The light source of claim 1located within an endoscope.
 24. The light source of claim 1 configuredas a self-contained source of illumination further comprising a batterypower source.
 25. A compact, high-efficiency, high-power, solid statelight source, comprising: a high-power solid state white light-emittingdiode (LED); a light guide comprising a bundle of a large number ofsmall diameter fibers, the bundle having an essentially flat proximallight-receiving end proximate the light-emitting device, and a distallight-transmitting end spaced farther from the light-emitting device;and a mechanical light guide fixing device coupled to the light guidenear its proximal end, to hold the proximal end of the light guide inposition directly against the light-emitting surface of the LED.